The present invention relates to the testing or monitoring of the function of a car radar.
In car radar systems, it is important to be able to test or monitor the function of the system during operation. It is relatively easy to test interior electric functions, e.g. by applying a test signal instead of the signal from the transceiver antenna unit of the car radar and evaluating the response of the system to this signal. However, testing of the actual transceiver antenna unit requires sophisticated testing equipment, which is placed separately in front of the car radar.
The object of the present invention is to provide a possibility of testing or monitoring a car radar, preferably of FMCW type, and in particular its transceiver antenna unit in a simplified and at the same time efficient way.
According to the invention, the above-mentioned object is achieved by a method, device and use having the features stated in the accompanying claims.
The basis of the invention is thus the understanding that it is advantageous to create opportunities for the desired testing inside the actual transceiver antenna unit. By exerting in a controlled manner an influence on the radar radiation in the actual beam path in the unit, i.e. in the beam path after the radar beam has left the microwave feeder of the unit, such as a horn, but before the radar beam leaves the unit, it is possible to generate reflected radar signals corresponding to a simulated target, which is located at a certain distance from the antenna unit. An evaluation of such simulated target signals results in target data, which can be related to target data, which can be expected in response to the tested, controlled influence on the radar radiation. As will be understood, a possible error function will easily be detectable, e.g. in the form of a deficient correspondence between the obtained simulated target data and the corresponding expected target data. The latter can be calculated or determined empirically.
According to the invention, said radar radiation influence can advantageously comprise the provision of a local radar radiation reflection in the unit with distinctly altered microwave parameters in relation to the normal reflection in the unit, in particular as concerns amplitude and preferably also phase when an FMCW radar is used.
According to a preferred embodiment of the invention, said controlled influence comprises the step of locally altering in the unit the impedance of a reflecting part to the radar radiation. The obtained alteration of the impedance will result in detectable signal variations in the receiver member of the car radar system, which variations can be evaluated as simulated target data.
In a preferred embodiment of the invention an FMCW radar is used, in particular with an antenna of the so-called Cassegrain type, with a fixed subreflector and a movable main reflector. The antenna unit of the radar transmits a radar signal, which is frequency-modulated, i.e. its frequency is varied linearly over time. The received, reflected radar signal is mixed with the transmitted one, resulting in a difference frequency. The latter is a measure of the time delay of the received signal and thus of the distance to a reflecting target. For signals that are normally reflected from the inside of the antenna unit, the time of propagation is so short that the difference frequency is zero in practical application.
By placing, in the beam path of the antenna unit, a reflecting part with a variable radar radiation impedance and influencing this impedance in a controlled manner, it is possible to influence the signal received in the antenna unit both as concerns phase and amplitude, hence simulating a target at a distance from the antenna unit. The resulting effect will be dependent on both the impedance variation of said part (resistive and reactive) and the exact positioning of said part in relation to the reference plane of the receiver in the antenna unit. As an example of the latter it can be mentioned that in a car radar system, which is operating with a wavelength of 4 mm, a displacement of said part with variable impedance by 0.5 mm will result in a rotation through 90xc2x0 of the resulting experienced modulation. In a corresponding manner, the experienced modulation will shift phase if the wave propagation in the antenna unit is changed. The latter is the case when the antenna unit contains a movable reflector element. This situation can then be used to check, when evaluating the simulated target signal, whether the reflector element moves correctly.
According to a preferred embodiment of the invention, the impedance variation of said part is modulated with a frequency corresponding to the difference frequency of a simulated target. The radar system will perceive this as there being a target at a corresponding distance from the antenna unit. By varying the modulating frequency, the simulated target can be moved to various distances. Likewise, targets of different intensity can be simulated by varying the modulation in respect of amplitude.
The reflecting part with variable radar radiation impedance is preferably a diode means. Its impedance can easily be varied by conducting an alternating current through the same. The radar radiation reaching the diode means will be reflected in different ways depending on the impedance of the diode means. In the radar receiver, this will be experienced as a variable target. The frequency of the alternating current can be selected such that it corresponds to the difference frequency of a simulated target, which is located at a certain distance of interest.
The diode means is preferably of the so-called PIN diode type. The diode means can be mounted on a printed circuit board, on which electronics associated with the antenna unit are mounted. With a view to improving the connection between the diode means and the microwave radiation incident on the same, it can be advantageous to use an extra coupling element in connection with the diode element. This coupling element can be can be formed as a conductive pattern in the printed circuit board tuned to the microwave frequency, or alternatively as a mechanical element, which is tuned to the microwave frequency, is mounted on the printed circuit board and has a certain vertical extent above the printed circuit board. Such an element can typically have a dimension in the order of 1 to 4 mm.
The invention makes it possible at a very reduced cost to easily solve the problems of testing a car radar system, at the same time as a number of advantages are achieved:
An overall testing of the transmitter, receiver and antenna (including the movements of the antenna) is made possible without exterior equipment;
It is an incorporated testing device which is an integrated part of the system;
Very few and cheap extra components are needed;
The testing device can be permanently present with-out disturbing the ordinary function;
Below the invention will be described in more detail by means of an embodiment and with reference to the accompanying drawings.